Not Applicable
Not Applicable
1. Field of the Invention
This invention pertains generally to plant fitness analysis, and more particularly to an apparatus and method for assessing plant nutrient needs by visually distinguishing color values from a color chart, calibrating a nutrient percentage according to plant variety, and assessing nutrient need according to the current position in the growth cycle. The user can thereby quantify the need and amount of soil supplements to avoid under or over-fertilization and maximize yields.
2. Description of the Background Art
The agriculture industry typically operates on relatively low profit margins and such profits may be lost by low crop yields. Low crop yields are particularly devastating to farmers in third world countries. Maximum crop yields may only be achieved through the regular monitoring of plant growing conditions throughout the growing cycle of the crop. Accurate monitoring of crop conditions allows the grower to adjust and plan for the application of fertilizer, schedule irrigation, identify the need for pesticides, estimate yields, and identify problems with planting.
Estimating tissue nitrogen (N) status at critical points of the life cycle of a plant can greatly improve the economics of agricultural plant production. For example, with rice and other grains, adequate levels of nitrogen are particularly critical during the onset of the reproductive phase. Kernel sizes, as well as the number of kernels per head, are sensitive to nitrogen levels in the plant.
Fertilizer applied during the early stages of the growth cycle may stimulate slower growing crops to reach normal levels of growth by the end of the growing cycle. However, excessive amounts of nitrogen fertilizer may actually reduce the quality and yield of certain crops. The excessive application of fertilizer may also result in contamination of waterways from irrigation runoff resulting in unwanted environmental effects. Furthermore, the untimely application of insufficient amounts of nitrogen fertilizer will have no appreciable effect on crop yield and is an additional uncompensated cost to the grower. Accordingly, the proper timing and amount of supplemental fertilizer to be applied to a crop is essential for optimum crop development and production efficiency.
The nitrogen levels in the most recently expanded leaf of rice, for example, have been shown to be a reliable indicator of the overall plant nutrient status. Once a nitrogen deficiency is identified, a grower needs to know the incremental increase in leaf nitrogen needed for optimum growth and the quantity of nitrogen fertilizer to be applied to achieve that increase. The grower must often estimate the actual amount of fertilizer that should be applied to the crop that is needed to raise leaf nitrogen into the adequate range. This invariably leads to the application of inadequate or excessive amounts of fertilizer during the growing cycle of the particular crop. In addition, the time interval during the reproductive phase where nitrogen fertilization is the most efficient is very short, often only a few days. Thus to be effective a grower must evaluate a large number of plants over the acreage and make management decisions within a short period of time.
Early methods for ascertaining the nitrogen content of a crop required the chemical analysis of the plants and the soil in a laboratory setting. The grower was required to take multiple samples, categorize and account for the samples, and submit the samples to a laboratory for testing. This process was time consuming and the delay in obtaining lab results often resulted in the grower missing the opportunity to apply fertilizer in a timely manner within the growing cycle of the plant.
Later, research on rice and other plant species demonstrated that leaf reflectance spectra could reliably predict leaf nitrogen concentration. Aerial and satellite photographs of the fields were utilized and compared with fields that had sufficient nitrogen. However, the satellite and aerial photographs provided limited information due to the low resolution of the photographs. The cost and the delay that occurs in taking and developing the photographs prohibited frequent use of the technique to monitor nitrogen during the growth cycle of the crops. Furthermore, the instrumentation used to measure color was not suitable for on-farm use, and predictive reflectance wavelengths were frequently outside of the visible range. Such techniques were also not available to the third world farmer.
Hand held chlorophyll meters, such as the Model SPAD-1504 made by Minolta Ltd., were developed to estimate leaf nitrogen, but these instruments are costly and require extensive sampling for accurate calibration before they are useful. In addition, these machines are prohibitively expensive and therefore unavailable to the third world grower.
Generalized color charts with various shades of green paint were developed for rice crops. However, the colors of these charts did not have the spectral reflectance characteristics of the plant nor were the colors correlated with a nutrient percentage, the plant growth cycle or a particular variety of rice.
Thus, a need exists for a reliable method of accurately determining the levels of nitrogen and other nutrients in crops that is immediate, inexpensive and easy to use. Furthermore, there is a need for a method of accurately predicting the amount of fertilizer that should be applied to a field that can be used daily and provide real time recommendations. The present invention satisfies those needs, as well as others, and overcomes the deficiencies of previous analytical apparatus and methods.
The present invention is a method and apparatus for determining the nitrogen status of a field crop such as rice. The apparatus comprises a leaf color chart, a calibration table, and an assessment chart.
The leaf color chart comprises a planar, rectangular, plastic support structure that carries a palette of eight different color cells with each cell having a different shade of green. The shades of green have been chosen such that they correlate to nitrogen content in the plant and have been developed through careful examination of the spectral characteristics of the plant leaf at different nitrogen states. The color cells have been configured to have virtually the same spectral reflectance characteristics as observed in certain plants. A marginal portion along the longitudinal edge of the plastic color chart is preferably removed to facilitate direct visual comparison between the crop and color panels.
The leaf color chart may be configured to have the specific spectral reflectance characteristics of a particular plant type such as rice or can be adapted to non-agricultural applications wherever a visual comparison of colors is required. While rice is used herein as an example of one embodiment of the invention, it will be understood by those skilled in the art that the invention can be adapted to grasses and plants other than rice.
The color of each cell of the leaf color chart is preferably determined by obtaining reflectance characteristics of the plant at different nitrogen levels that are described in three-dimensional color space having a luminescence coordinate (L), a red to green scale coordinate (a*) and a blue to yellow scale coordinate (b*). Spectral reflectance characteristics are preferably obtained over the visible spectrum of approximately 400 nm to approximately 700 nm in approximately 10 nm increments. This creates a spectral profile of the plant. The spectral characteristics of the fabricated color cells are preferably tested repeatedly to ensure that leaf color is accurately described. Additionally, the leaf samples are preferably chemically analyzed for total nitrogen content.
The calibration table comprises an array of nitrogen or other nutrient level entries, the columns of which are indexed according to a unique identifying number associated with each color cell, and the rows of which are indexed by the variety of rice or other plant type. Use of the calibration chart provides a leaf nitrogen level value in percent. A separate calibration table is preferably provided for each nutrient such as potassium, magnesium, phosphorous nitrogen and the like.
The assessment chart comprises a graph of nitrogen status based on the leaf nitrogen level value derived from the calibration chart compared to the plant growth stage for the subject plant variety. Various color shades on the chart indicate the nitrogen status of the crop, as being adequate, critical, deficient, or excessive. Like assessment charts are provided for other nutrients of interest.
According to the invention, a sample leaf is taken from the field and placed on the leaf color chart panel that has substantially the same color as the leaf. The leaf chart panel number is then matched to the variety calibration chart to determine the nitrogen percent value for the leaf for the variety of plant. A nitrogen assessment is obtained by placing the percent nitrogen value on an assessment chart at a point determined by the stage of growth of a particular plant variety. The percent nitrogen is then assessed as adequate, critical, deficient or excessive, thereby allowing decisions to be made regarding fertilization.
An object of the invention is to provide a method of analyzing the nitrogen or other nutrient content of a crop that provides relevant data in real time and accurately identifies the quantities of fertilizer necessary to optimize the growth of the crop.
Another object of the invention is to provide a method for identifying nitrogen ad other nutrient needs and fertilizer quantities that is easy to use and can be used on a daily basis throughout the growing cycle of the crop.
Another object of the invention is to provide a color chart that has essentially the same spectral reflectivity as the crop at various nitrogen states.
Yet another object of the invention is to provide a method for accurately correlating spectral reflectance data with fertilizer needs that is inexpensive to manufacture and use.
A further object of the invention is to provide a method of creating a color chart that can be tailored to a particular plant type.
Further objects and advantages of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the invention without placing limitations thereon.